Metallurgical process



patented @eta 5, i937 naar ifi METALLURGICAL PRCIESS Application )December 3, 1934, Serial No. 55,'l26

6 Claims.

The present invention provides an improved process for the treatment of metalliferous materials, such as metallurgical by-products, scrap, ores, and the like wherein the materials, in suitable condition, are subjected to a leaching solution of such composition as will dissolve the values, which are then recovered from the solution in a direct and economical manner.

More spccically, the invention provides a hydro-metallurgical process for the recovery of tin, which process may be applied to a wide variety of tin-bearing materials, including by-products from scrap treatment, tin ores, including low grade ores, and, in general, any stanniferous material in which the tin is present in a form convertible to metal, the present process then being applicable for the rening and recovery of the tin in a condition of very high purity.

One of the objects of the present invention is to provide a process wherein the tin-bearing material is eiciently extracted by a suitable solvent, from which the tin may be recovered in an exceptionally high state of purity, and in an economical manner.

A further object of the invention is to provide a leaching process for the extraction of tin from tin-bearing materials from which the tin may be economically extracted in a high state of purity, and in which the leach liquid may be easily and efficiently regenerated.

Further objects and advantages of the invention will become apparent as the description proceeds, the features of novelty being pointed out in the appended claims.

Before proceeding with a specilic illustration of the present improved process, it is thought to be desirable to review, generally, the various steps of the procedure.

Although applicable to tin-bearing4 materials generally, wherein the tin is present in metallic state, the present process is designed especially for the recovery of tin in a high degree of purity from by-products resulting from the treatment of scrap materials, such as, for example, scrap combustion engine radiators; and the process will be described as applied to the recovery of tin from the sources just indicated above, although it is to be borne in mind that the process is of widely generall adaptation to materials containing tin in metallic form. y

In accordance with the practice of the process as applied to scrap radiators and the likefthe scrap is first subjected to a sweating operation in suitable furnaces, whereby a certain amount of the solder associated with the scrap is melted (Cl. 20d-57) off and collected in a directly marketable condition.

A certain amount of the solder becomes alloyed with the copper of the radiators and to recover this alloyed solder the radiators, after being sweated, are-briquetted and then sent on to a melt down furnace, for melting. The supply of material in the melt down furnace may be augmented by the addition of scrap composition brasses and bronzes and also with impure copper from the blast furnace, this copper containing considerable tin and/or lead and other impurities.

The alloyed materials from the melting furnace are then sent to a, converter and blown with air under a suitable flux comprising, for example, soda ash, sand and fluorspanalthough other iluxing materials may be employed. The converter is rotated and the charge is blown with air to eliminate the zinc as fume. 'I'he blowing also oxidizes a part of the tin and copper present, together with the lead, the resulting oxides being transferred into the flux to form a slag or dross. This slag or dross is separated from the remainder of the charge in the converter, which remaining charge is blister copper which is sent to the refinery for the refining into electrolytic copper. The slag or dross separated from the blister copper of the converter is sent to a reverberatory furnace or it is smeltedto metal with coke, and a discard slag is formed.

'Ihe metal thus produced forms a valuable byproduct because of its high tin and copper contents, and it is readily treated by the present lmproved process for recovering high-grade tin therefrom.

In order to renne this by-product, it is first reduced to metallic form by smeltingv with coke. A typical analysis of the reduced metal is:

Sn 42% :840 lbs. Sn/ton Cu 43.4 %=878 lbs. C11/ton Pb 9.0 %=180 lbs. Pb/ton Fe 0.9 18 lbs. Fe/ton Sb 0.8 16 lbs. Sb/ton Zn 0.36%=7.2 lbs. Zn/ton Ni Nl/ton 0.12%:24 ibs.

but the presence of copper sulphate produces a whollyunexpected leaching efliciency, the copper sulphate resulting in a leaching eihciency of 90% or better, which is at least double that obtainable by sulphuric acid alone. It has been observed, however, that the tin extracted from the metal tends to hydrolyze in the leach solution, but it has been found that the hydrolysis of the tin is preventedby the addition of suitable quantities of non-hydrolyzing soluble sulphates, for example, sodium sulphate or potassium sulphate, which are accordingly desirably present in the leaching solution.

'I'he leaching is desirably carried out by heating materials during the leaching operation, the temperature and time of leach being controlled so as to prevent substantial hydrolysis of the resulting tin solution,tests having shown that while sodium sulphate and other soluble sulphates prevent hydrolysis of the tin solution up to a certain point, excessive heating or excessively prolonged contact of the metal with the leaching solution will hydrolyze the tin, notwithstanding the presence ofthe sulphate. Tests on this point have shown that sodium sulphate deiinitely prevents hydrolysis of the tin if the solution thereof is not heated above approximately '70 C. and if the time of leaching does not exceed approximately one hour. Too high temperatures and/or too long a leaching time produce hydrolysis of the tin notwithstanding the presence of the sodium sulphate thereby causing excessive tin losses and rendering iiltration diiicult.

In order to eiiect a thorough contact between the leaching solution and the metal, it has been found in practice to be desirable to introduce the metal and the leaching solution into a pebble mill containing flint pebbles as in this way a most intimate contact is effected by the grinding action imparted by operation of the mill. Certain distinct advantages are obtained by the use of a pebble mill over the use of a ball mill for this purpose, for the steel balls of a ball mill become coated with lead sulphate, and there is also an inevitable solvent action on the balls by the leaching solution. This solvent action of the leaching solution on the iron of the balls precipitates out the copper from the copper sulphate leaching solution before the tin in the metal being treated has a chance to act, and in view of the fact that the efciency of the leaching action of the copper sulphate on the tin is dependent largely on the interchange between tin and copper, the precipitation of the copper by the iron of the balls would largely destroy the eiectiveness of the copper sulphate as a tin leaching material. Both of the above-mentioned objections are obviated by the use of the pebbles. It is found in practice that a 90% extraction of the tin, or better, isV obtained, actually, in a leaching time of from twenty minutes to half an hour.

The leaching itself may be eected in any suitable manner, as in leaching tanks using the counter-current principle, or in a revolving drum,l also using the counter-current principle, the leaching solution being passed in a direction counter to the direction of travel of the material so that there will be an excess of sulphate solution at one end of the leaching apparatus and excess of metal at the other end.

During the leaching, tin Passes into solution from the metal being leached, displacing an equivalent amount of copper from the solution:

From the leaching system, the solution and solids are passed to a settling tank, Where an initial clarilication of the solution is elected, the clarification being completed by filter pressing.

The claried solution, containing the extracted tin in solution, is sent on to electrolytic cells, the solution being electr/olyzed using desirably, insoluble anodes (graphite or lead) and cathodes of sheet tin. A suitable addition agent may be used in the electrolyte for obtaining a good deposit of tin, as, for example, glue and cresylic acid in substantially equal proportions.

The tin cathodes with their resulting deposit of tin are melted and cast into bars for marketing. The tin thus produced is of exceptionally high quality.

'I'he stripped electrolyte is open to several possible treatments:

(1) 'I'he entire amount of the stripped electrolyte may be mixed with the enriched copperbearing residue from the leaching operation, thereby regenerating the leaching solution by solution of the copper, the regeneration being effected desirably in a Pachuca tank with. the aid of compressed air and steam which render the copper readily soluble in the stripped sulphate electrolyte, now consisting essentially of sulphuric acid.

2) If impurities, such as iron for example, have built up in the electrolyte to such an extent as to depress unduly the deposition of the tin, the stripped electrolyte may be divided and a portion thereof sent to the Pachuca tank, the remainder being treated with hydrogen sulphide to precipitate the tin as sulphide, which may be filtered 01T, roasted to oxide and smelted down to metal, the liquid from 4the sulphide precipitation being discarded.

(3) A third mode of treatment would be, under the conditions of (2) above, to precipitate the entire volume of stripped electrolyte with hydrogen sulphide, with subsequent treatment of the precipitated SnS as indicated under (2) above, and discarding the liquid. In this event, fresh leaching solution would be regenerated in the Pachuca tank by the addition of sulphuric acid thereto in quantities suflicient to dissolve the copper.

f course the step of electrodeposition of the tin could be entirely replaced, if desired, by the sulphide precipitation above outlined, or by any other Way of recovering tin from the sulphate solution; but experience indicates that such substitution can be made only at the sacrifice of eiciency and economy, it being found in practice that the electrolysis of the tin-bearing solution is the most direct and economical method, and producing tin of the highest degree of purity.

The material from the Pachuca tank is ltered, the residue being suitably smelted to produce a metal suitable for releaching by the process as above indicated, while the regenerated leaching liquid is returned for re-use. with the addition of sulphuric acid and/or sodium sulphate as may be required.

It will thus be seen that the process is fully cyclic, and in actual practice it operates easily and with a high efliciency throughout the various steps.

Instead of sending the entire residue from the cie example of the process, which example will beunderstood as being purelyillustrative of the process and in no sense limiting thereof, and since the preparation of the metal to be treated forms no part of the present invention except in general combination with the steps of the novel procedure, the detailed description of the procedure illustrated by the now sheet will be begun with the treatment ofthe metal itself.

' In accordance with the illustration shown in the drawing, one'ton of metal, to be reiinedand ground to a suitable neness is leached with 400 cubic feet or 11,300 vliters of leaching liquor. The metal may have the typical composition previously indicated herein, i. e.:

Sn 42%:840 lbs/ton Cu 43.2%:8'78 lbs/ton Pb 9.0%:180 lbs/ton Fe 0.9%:18 lbs/ ton Sb 0.8%:16 lbs/ton Zn 0.36%:72 lbs/ton Ni 0.12%=2.4 lbs/ton The leaching liquor may have the typical cornposition: H2SO4 105 gms./liter=2609 pounds in the 11,300 liters used; Na2SO4 (to prevent hydrolysis of the dissolved, tin) 101 gms./liter=` 2510 pounds; Cu as CuSOi. 20.2'gms./liter=505 pounds? Sn as SnSO4 10 gms./liter==249 pounds. This tin, of course, is not present in the fresh leaching solution, but represents accumulated residual tin resulting from'recycling the solution, the presence of which is accounted for by not obtaining an absolutely complete precipitation of the tin in the electrolytic cells. The quantity of the leaching solution and its composition are largely dependent upon the composition of the metal being refined.

The leaching liquor and metal to berefned are brought together in an agitator or revolving drum. Practice has shown thatv the highest eiliciency of the leaching is obtained by using a revolving drum or pebble mill vusing flint pebbles,

the leaching being performed on the counter-- current principle, as above indicated, and the mixture being heated to approximately` '70 C. to expedite the solvent action. If the leaching is performed in agitating tanks, practice indicates that a very iine grinding of the metal should be resorted to, 300 mesh being necessary for greatest leaching efficiency. If the leaching is performed in 'a revolving drum or pebble mill,v

the grinding need not be carried so far. At approximately 70 C., a leaching time of about one hour is found to be suflcient. During the leaching operation, the tin from the metal being treated goes into solution, precipitating equivalent amounts of copper.

From the leaching system, the materials pass to a settling tank where an initial clarification of the solution is effected. The liquid usually remains turbid, however, so that a iilter press is usually connected with the settling tank, so that the solution can be run immediately through the filter press.

This procedure separates the materials intoI a solid residue and a filtrate. The residue analyzes, typically, Pb 180 pounds as PbSOi (85 pounds H2504); Cu 1345 pounds metallic; Fe

Sn 995 pounds=40 gms/liter y HzSOfi 2490 pounds-100 gms/liter Naz'SOi 2490 pounds=l00 gms/liter Fe 249 pounds.: 10 gms/liter Ni 40 pounds=l.6 gms./liter This iiltrate is passed to electrolytic cells, where 'it is electrolyzed, using preferably insoluble anodes of graphite or lead, for example, and catlicdes ot'sheet tin. Typical electrolysis data may be indicated as follows: A

Cell voltage=2.1^volt s Current consumption=317 K. W. H. at room temperature, or 917 K. W. H. per ton Ampere emciency=93.7%

'Ihe electrolysis is carriedjout preferably in the presence of a suitable addition"agent, such as glue and cresol in equalamounts of 'l vpounds for the indicated quantity of electrolyte.

The tin deposits on the cathodes under the above conditions in a good deposit of very high purity. Under the above conditions, the'weight of the tin deposit was found to bev 63d pounds. The tin is melted in a suitable melting pot and cast into bars for sale or other desired disposition.

The stripped electrolyte contains approximately 3200 pounds of H2SO4, or 129 gms./liter. `'llhis stripped electrolyte is mixed with the residue in a Pachuca tank, where themetallic copper of the residue is dissolved by the stripped electrolyte with the aid of compressed air and steam.. introduced into the Pachuca tank from. a suitable source.

The resulting solution and residue-from the Pachuca tank is passed through a filter press, where the regenerated leaching solution and the residue are separated. l

The residue is returned to the converter for re-treatment and ire-conversion into' metal for retrmtment.

The solution, amounting to approximately 400 cubic feet, including water condensed from the steam of the Pachuca tank, contains approximately: H2SO4 2262 pounds; NazSO4 2365 pounds;

Cu 505 pounds; Sn 249 pounds. This tin` is residual tin, undeposited in the electrolytic cells.

In order to make up the desired concentration ofl leaching solution lfor re-use, and to replace the materials lost from the cycle by the regular discarding of part of the electrolyte, there were added approximately 347 pounds-MS04 equivalent to 450 pounds of 60 B. acid and 150 pounds of NazSOi, the resulting solution being then reused.

As indicated above, if impurities such as iron build up in the electrolyte to an extent adversely effecting the deposition of the tin, the remaining tin may be precipitated with hydrogen sulphide,

' which, in the acid solution present, will not throw tin-bearing materials being capable of being treated by this process, individual steps of which may be modified, of course, as may be determined by particular operation conditions. Low grade tin ores may be treated for the recovery of the tin by subjecting them to a reducing roast to produce metallic tin and then leaching the reduced roast with copper sulphate in a revolving drum.

The process may be adapted for the treatment of materials other than tin-containing materials, as any metallic material electropositive to copper nay be rendered amenable to treatment in acordance with this general process and from the above description, it will become apparent that many details of operation may be modified to meet particular conditions of operation without departing from the inventive concept; it will be understood accordingly that itis intended and desired to embrace within the scope of this invention such modifications and changes as may be necessary to adapt it to varying conditions and uses.

IWhat is claimed is:

1. A process of recovering the values from scrap combustion engine radiators and the like which comprises melting scrap radiator material, transferring the resulting molten alloy material to a converter, blowing the said material to blister copper with attendant formation of a slag rich in tin and copper, with smaller quantities of lead, separating the said slag from the blister copper, smelting the said slag to produce an alloy metal rich in tin and copper, leaching the said metal With copper sulphate solution to dissolve the tin, and recovering the tin from the resulting tincontaining solution.

2. A process of recovering the values from scrap combustion engine radiators which comprises melting scrap radiator material, transferring the resulting molten alloy material to a converter, blowing the said material to blister copper with attendant formation of a slag rich in tin and copper with smaller quantities of lead, separating the said slag to produce an alloy metal rich in tin and copper, leaching the said metal with copper sulphate solution in the presence of suicient sodium sulphate to prevent hydrolysis of the tin dissolved by the copper sulphate, and recovering the tin from the resulting tin-containing solution.

3. A process of recovering the values from scrap combustion engine radiators which comprises melting scrap radiator material, transferring the resulting molten alloy material to a con-v verter, blowing the said material to blister copper with attendant formation of a slag rich in tin and copper with smaller quantities of lead, separating the said slag to produce a brittle alloy metal rich in tin and copper, leaching the said metal with copper sulphate solution in the presence of suiiicient sodium sulphate to prevent hydrolysis of the tin dissolved by the copper sulphate, recovering the tin from the resulting tincontaining solution, and regenerating the copper sulphate solution for leaching further quantities of the said metals.

4. A process 'of recovering tin from impureV proximately 40% of tin which comprises dissolving the tin with copper sulphate solution containing suilicient sodium sulphate to prevent hydrolysis of the tin dissolved by the copper sulphate, the solution of the tin being accompanied by precipitation of equivalent amounts of copper from the copper sulphate, recovering the tiri from the resulting tin-containing solution, and contacting the resulting stripped solution with the precipitated copper under conditions effecting solution of the copper with consequent regeneration of the said copper sulphate solution adapted to dissolve fresh quantities of tin from the said alloys.

6. A process of recovering the values from scrap combustion engine radiators and the like which comprises melting scrap radiator material, transferring the resulting molten alloy material to a converter, blowing the said material to blister copper with attendant formation of a slag rich in tin and copper with smaller quantities of lead, separating the said slag from the blister copper, smelting the said slag to produce an alloy metal rich in tin and copper, leaching the said metal with copper sulphate solution to dissolve the tin with attendant precipitation of copper, electrolyzing the resulting tin solution under conditions effecting dense, adherent deposits of tin, and contacting the resulting stripped electrolyte with the precipitated copper under conditions effecting solution thereof to regenerate the said copper sulphate solution.

JESSE O. BETTERTON. GEORGE K. BAUMANN. 

